- Person
- Lise Meitner
- Lived
- 1878–1968
- Field
- Physics
- From
- Austrian-Swedish
The story
By 1917 Lise Meitner had worked with the chemist Otto Hahn in Berlin for a decade, and in January of that year she was made head of her own physics section at the Kaiser Wilhelm Institute for Chemistry. One problem left over from their pre-war research was the search for the parent of the element actinium. According to the rules of radioactive decay, it had to be an isotope of the still-missing element 91, between thorium and uranium on the periodic table. In 1913 Kasimir Fajans and Oswald Göhring had found a short-lived isotope of element 91 and called it brevium, but it could not be actinium's parent.
With Hahn and most of the students, assistants and technicians called up for military service, Meitner had to carry out the search almost entirely by herself. In February 1917 she extracted silicon dioxide from 21 grams of pitchblende ore, dissolved and precipitated it, and showed that the product was an alpha emitter. When Hahn came home on leave in April, they devised tests to rule out other known sources of alpha particles.
She needed more material. Wartime rules banned the export of uranium from Austria, but in Vienna Stefan Meyer gave her a kilogram of uranium residue, which was actually better for her purposes. Later she obtained a further 100 grams of residue from Friedrich Giesel, who helped her produce a pure, strongly radioactive sample. By December 1917 she had isolated both the parent isotope and its actinium daughter, and the findings were submitted for publication in March 1918.
Custom required that an element be represented by its longest-lived isotope, and brevium no longer seemed appropriate. Fajans agreed to Meitner's proposal to name the element protoactinium, meaning the precursor of actinium, later shortened to protactinium, with the symbol Pa. In June 1918 Frederick Soddy and John Cranston in Britain announced an independent sample, acknowledged Meitner's priority and accepted the name, which the international chemistry union confirmed in 1949.
The discovery filled one of the last gaps in the periodic table of the time. The isotope she found, protactinium-231, has a half-life of about 32,760 years, and today scientists use it alongside thorium to date ocean sediments up to 175,000 years old, helping to reconstruct how ocean currents changed at the end of the last Ice Age.
Why it matters
Meitner's painstaking wartime work filled a gap in the periodic table, and the isotope she found is now used to date ocean sediments and reconstruct past climates.
About Lise Meitner
Nuclear physicist who co-discovered nuclear fission; refused to work on the atomic bomb. Element 109 (meitnerium) named for her.
More about Lise Meitner
- Lise Meitner explained and named nuclear fissionLise Meitner and her nephew Otto Frisch were the first to explain how a uranium nucleus splits, and in a 1939 paper in Nature they named the process "fission".
- Lise Meitner discovered what is now the Auger–Meitner effectIn 1922 Lise Meitner explained why atoms emit electrons with signature energies. The process is now called the Auger–Meitner effect after her and Pierre Auger.
- Lise Meitner became Germany's first woman physics professorIn 1926 Lise Meitner became the first woman university professor of physics in Germany, after starting her Berlin career as an unpaid guest in a converted woodshop.
- Lise Meitner refused to help build the atomic bombAlthough her work explained nuclear fission, Lise Meitner declined an invitation to join the British mission to the Manhattan Project, saying she would have nothing to do with a bomb.
- Lise Meitner served as an X-ray nurse in World War IDuring the First World War, Lise Meitner trained as an X-ray technician and served with the Austrian Army as an X-ray nurse on the Eastern and Italian fronts.
Sources
- Lise Meitner Wikipedia
- Protactinium Wikipedia
Another act of tikkun olam. This is part of tikkun olam, the Jewish idea of repairing the world, and every one of us can add to it.